Moving object radio pulse-echo system



Feb. 27, 1951 A. G. EMSLIE 2,543,448

' uovmc OBJECT RADIO PULSE-ECHO svs'rsu Filed May 17, 1945 I ll [I3TRANSMITTER )2 7 T- R l-F o "2 MIXER ECHO v. ECHO 5 BOX BOX A F, t l-F vI F 2| MIXER l9 MULTIPLIER AMPLIFIER/ SYNCHRONIZED OSCILLATOR 5 ETECTOR'8 INDICATOTIZ3 INVENTOR. ALFRED G- EMSLIE AT TORNEY Patented m. 27,195i MOVING OBJECT RADIO PIlLSE-ECHO SYSTEM Alfred G. Emslie, Boston,Mass., assignor, by mesne assignments, to the United States of Americaas represented by the Secretary of War Application May 1'7, 1945, SerialNo; 594,262

3 Claims.

The present invention relates to radio objectlocating systems adapted todistinguish fixed objects from moving objects, and it relates moreparticularly to a coherent pulse-echo system wherein anintermediate-frequency synchronizing pulse is obtained without the useof a local oscillator.

A coherent pulse-echo system is a. radio object-locating systemcharacterized by continuous wave or interrupted continuous wavereference oscillations (sometimes hereinafter called a timing wave),synchronized in fixed phase relation (in coherence) to the usualtransmitted exploratory pulses. By algebraically combining the referenceoscillations and the echo-pulses returned from a reflecting obiect, anddetecting the envelope of the resulting combination, video pulses may beobtained which provide velocity information. The object-returnedecho-pulses, w n added to the reference oscil ations. will reinforce oroppose said reference osci'lations, the reinforcing or opposing action,depending upon the phase relation between the two.

Succeeding echo-pulses returning from a fixed object will always havethe same phase relation with respect to the reference oscillations, andwhen combined with said reference oscillations will provideconstant-amplitude video pulses. vOn the other hand. succeedingechopulses from moving objects will have a progressive phase shift withrespect to the timing wave, and when combined therewith. will providevideo pulses having a cyc ical variation in amplitude. The presentationof these video pulses, by either visual or aural means, will provide amethod whereby fixed ohiects can -be readily distinguished from movingobiects, and, in the case of the latter, will indicate the objectvelocity relative to the exploratory pulse transmitter.

If desired. obiect-returned echo-pulses may be combined directly with atiming .wave whose frequency is substantiall equal to-thecarrier-frequency of the exploratory pu ses. The term carrier-frequencyof a pulse as here used refers to the center frequency of the band offrequencies contained in a pulse. In general, however, better resultsare obtained if the timing wave and echo-pulses are combined at anintermediatefrequency (called intermediate-frequency coherence). A moredetailed explanation of a coherent pulse-echo system employingintermediate frequency coherence is described in a copending applicationof Robert H. Dicke, Serial No. 590,052, filed April 24, 1945.

Hereinafter the portion of each exploratory vide an improved coherentpulse-echo system wherein a synchronizing pulse having anintermediate-frequency carrier wave is ob ained in a simple and reliablemanner, and without the use of a local oscillator for this purpose.

It is another object of the present invention to provide an improvedcoherent pulse-echo system employing intermediate-frequency coherencewherein resonant cavities are utilized to provide a synchronizing pulsehaving an intermediate-frequency carrier wave.

The above and other obiects and advantages will appear more fully in thefollowing description, taken with the accompanying drawing wherein thesin le figure shows a schematic diagram, in block diagram form, of onespecific embodiment of the invention.

Referring now to the drawing, a transmitter H), which may be a magnetronor other suitable ultra-high frequency generator is adapted to provideshort duration, high carrier-fre uency, pulses of radiant energy, Pulsetransmission to a directional antenna ll may be achieved by suitabletransmission line l2, together with a customary transmit-receive switchl3.

Transmit-receive switch l3 functions to connect transmitter ill toantenna ll during transmission of exploratory pulses and to disconnectthe rest of the circuit shown. During the interim between pulses, theswitch functions to disconnect antenna II from transmitter in and toconnect antenna II to the receiver channel presently to be described.

A portion of the transmitted exploratory pulses is appliedsimultaneously to echo-boxes 14 and IS. The respective echo-boxes aretuned resonant cavities, having a high Q characteristic, that, whenexcited by radiant energy containing frequencies equal to the resonantfrequencies of the cavities, will each transmit or pass a pulse having avery narrow frequency spectrum.

Echo-box l4 and echo-box I5 are tuned so that and echo-box l5 may betuned to resonate at a frequency of The pulses issuing from saidecho-boxes will then consist of pulses having their carrier-waves atthese respective frequencies. Inasmuch as the echo-boxes are excited bythe side bands of the exploratory pulses, the operation of such a systemis facilitated by the use of vory short duration exploratory pulseswhich provide the necessary energy in the frequency side bands.

The pulse outputs from echo-boxes and I respectively are applied tomixer I5, the output circuit of which is tuned to a frequency equal tothe difference of the two input frequencies (the I.-F. frequency). Theoutput pulse from mixer l6, hereinafter referred to as the synchronizing(or locking) pulse, is applied to coherent oscillator IT. The coherentoscillator i1 is an intermediate-frequency oscillator, the output ofwhich is locked in fixed phase relation with respect to the exploratorypulses through the medium of the applied synchronizing pulses.

Oscillator IT has two outputs, one of which is applied as a timing waveto detector IS, the second output being applied to frequency'multiplieriii. The character and function of frequency multiplier I9 is more fullydescribed in a copending application of Alfred G. Emslie, Serial No.594,263. filed May 17, 1945. Briefly, frequency multiplier l9 acts toprovide stable oscillations whose frequency is substantially equal tothe exploratory pulse carrier-frequency, plus or minus theintermediate-frequency the choice of plus or minus being arbitrary.

Object-returned echo-pulses (having a carrierfrequency F0) received byantenna II are fed through transmit-receive switch [3 to mixer 20, asecond input to mixer 20 comprising the stable oscillations fromfrequency multiplier IS. The output circuit of mixer 20 is tuned to thedifference of the two input frequencies. Issuing from mixer 20,therefore, are object-returned echopulses having anintermediate-frequency carrierwave. These object-returned echo-pulsesmay then be applied to intermediate-frequency amplifier 2|, theamplified pulse output therefrom being applied as a second input todetector l8.

In detector l8 the reference oscillations from oscillator l1 and theecho-pulses from intermediate-frequency amplifier 2! are algebraicallycombined, and the envelope of the resulting combination obtained, toproduce video pulses.

Fixed objects will be manifested by constant amplitude video pulses, asmentioned above, whereas moving objects will be manifested by videopulses having a cyclical variation in amplitude. Video pulses fromdetector l8 may be utilized by an aural or vi ual indicator such asindicator 23 to readily distinguish fixed objects from moving objects,and to provide velocity information in the instance of the latter. Thenature of the velocity information contained in the video pulse and onepossible indicator is described in the above-mentioned copendingapplication of Robert H. Dicke, Serial No. 590,052, filed April 24,1945, issued as Patent No. 2,535,274 on December 26, 1950.

While there has been described one embodiment of the present inventionit will be manifest to those skilled in the art that various changes andmodifications may be made therein without departing from'the inventionand it is therefore aimed in the ap ended claims to cover all suchchanges and modifications as fall within the spirit and scope of theinvention.

I claim:

1. A radio object-location system, including means for generating andtransmitting short duration, high carrier-frequency exploratory pulsesof radiant energy, two resonant cavities tuned to different re onantfrequencies, means for simultaneously applying to said re onant cavitiesa portion of each of said exploratory pulses, the output from each ofsaid re onant cavities comprising a pul e having a carrier wave who efrequency is substant ally equal to the resonant frequency of itsassociated cavity, a mixer, and means for applying as inputs to saidmixer the outp t pul es from said resonant cavities, means for obtainingas an output from said mixer a synchronizing pulse whosecarrier-frequency is equal to the difference of the carrier-frequenciesof the input pulses thereto, an oscillator whose fre uency ofoscillations is substant ally equal to the carrier-frequency of saidsynchronizing pulse, means for synchronizing said oscillator with saidsynchronizing pul e, means for receiving object-returned echo-pulses,means including a frequency multiplier for reducing thecarrier-frequency of the obiect-returned echo-pul es to a frequencysubstantially equal to the frequency of the oscillator output, means forcombining the oscillator output and the reduced carrier-frequencyobiect-returned echo-pul es to obtain a voltage, means for detecting theenvelope of said voltage to obtain video pulses whereby the character ofsaid video pulses provides obiect velocity information.

2. A radio obiectlocation sy tem including means for generating andtransmitting short duration, high carrier-frequency exploratory pulsesof radiant energy, a reference oscillator providing an oscillatoryvoltage out ut, a plurality of resonant cavities and means for applyingthereto a portion of said exploratory pulses, means for obtaining fromsaid resonant cavities a synchronizing pulse whose carrier-frequency issubstantially equal to the frequency of the output from said re erenceoscillator, means for synchronizing said reference oscillator with thesynchronizing pulse, means for receiving object-returned echo-pulses,means for reducing the carrier-frequency of the object-returnedechopulses to a frequency substantially equal to that of said referenceoscillator, means for combining the output of said reference oscillatorand the reduced carrier-frequency echo-pulses to obtain an oscillatoryvoltage, means for detecting the envelope of said oscillatory voltage toobtain video pulses, the character of said video pulses providing objectvelocity information.

3. A radio object-location system including means for generating andtransmitting short duration, high carrier-frequency exploratory pulsesof radiant energy. a reference oscillator providing an oscillatoryvoltage output, a plurality ofresonant cavities and means for applyingthereto a portion of said exploratory pulses, means for obtainingfromsaid resonant cavities a synchronizing pulse whose carrier-frequency issubstantially equal to the frequency of the output from said referenceoscillator, means for synchronizing said reference oscillator with thesynchronizing pulse, means for receiving object-returned echo-pulses,means for combining the output 0! said reference oscillator and thereceived echo-pulses to obtain an oscillatory voltage, means fordetecting the envelope of said oscillatory voltage to obtain videopulses, the character of said video pulses providing object velocityinformation.

ALFRED G. EMSLIE.

6 REFERENCES crrnn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,750,668 Green Mar. 18, 19301,945,952 Nicolson Feb. 6, 1934 2,223,224 Newhouse Nov. 26, 19402,253,589 Southworth Aug. 26, 1941 2,268,587 Guanella Jan. 6, 1942

